There are known devices of the general type referred to, for instance, from my prior pending application Ser. No. 471,413 filed June 7, 1974 which comprise two rotatable drums and two superimposed and parallel power driven filter bands for continuously feeding sludge to be dewatered, preferably in the shape of sludge cakes, between the filter bands and for removing the sludge cakes after dewatering thereof. These bands are guided over parts of the cylindrical walls of the drums with pressure engagement in a manner so that the two drums are rotated in opposite directions. As a result of the pressure engagement of the bands with the drum walls water is pressed out of the sludge cake and escapes through the filter bands. Moreover, the filter bands are guided so that the inner filter band on the first drum becomes the outer filter band on the second drum, and vice versa, thereby further causing escape of water from the cakes.